Microporous membranes, including zeolite membranes, silica membranes, carbon membranes, and microporous polymeric membranes, have shown excellent gas mixture separation performance and may have wide applications in many industrially important separation processes. Current microporous membranes, however, are usually thick (thickness greater than 20 nm) in order to minimize flux contribution through non-selective defects and maintain reasonable separation selectivity. Further reducing membrane thickness to sub-20 nm range to lower transport resistance without introducing extra non-selective defects is highly challenging for current microporous membranes. This challenge may result from the limitations of membrane materials and/or membrane preparation techniques.
Graphene-based materials, such as graphene and graphene oxide (GO), have been considered as a promising membrane material, because they are only one carbon atom thick, and thus may form the thinnest separation membranes to maximize flux. Besides, they have good stability and strong mechanical strength. However, these graphene-based materials have been found to be impermeable to small gas molecules. Extensive simulation studies, therefore, have been conducted to understand effects of various potential defects or artificially generated “holes” on permeation behaviors of molecules and to predict mixture separation performance. Very recently, others reported an etched graphene by UV-induced oxidation to create pores, and found that the transport rates of H2 and CO2 were 3 to 4 orders of magnitude higher than N2 and CH4 through porous graphene flakes.
However, no practical graphene-based separation membranes have been prepared for studying their separation potential for gas mixtures.